    [Patent Literature 1] JP-2003-240628 A (US 2003/0154805 A1)    [Patent Literature 2] JP-H09-207638 A
In order to control inflation of an airbag, it is desirable to (i) recognize beforehand the physical size of an occupant, who is to be protected and (ii) control an inflation mode of the airbag. To that end, a load sensor has been built into a vehicle or a seat in the vehicle to provide an output voltage according to a load due to an occupant. The output voltage is then classified into one of classes (i.e., states) including a vacant seat class, a child class, an adult class, etc. based on predetermined threshold loads.
The output of a load sensor changes according to the change in occupant's posture or an acceleration G due to travel motion of the vehicle. The resultant change in the output of the load sensor further provides the temporary output of incorrect determination when threshold values are fixed.
Patent Literature 1 discloses a technology to overcome such an issue, for example. The technology includes a load sensor to detect a load, which is applied to a seat in a vehicle; and a determination section to determine (i) presence or absence of an occupant and (ii) the physical size of the occupant, if present, by classifying the detected load into one of several classes using predetermined class threshold loads. When a detected load continuously remains in a subject class among a plurality of classes longer than a predetermined threshold time (duration), it is determined that an inter-class transition into the subject class has arisen. Further, mutually different predetermined threshold times are prepared for at least some of the inter-class transitions.
Incidentally, in order to improve occupant protection, the number of classes of occupant physical sizes tends to increase to realize an airbag control that can respond to an individual occupant physical size. To that end, an occupant determination apparatus is also required to prepare multiple classes of occupants or their physical sizes.
In addition, four load sensors may be disposed in a leg portion of a vehicle seat for detecting all the loads applied to the seat. In contrast, Patent Literature 2 proposes a technology to reduce the number of load sensors from four to two.